North African nations put up novel barriers against growing desert

An invasion of insect pests is endangering North Africa's "green dam." This green belt of billions of drought-resistant cypress and pine saplings is being established to protect the region's fragile environment from encroachment by the Sahara Desert.

Much of the terrain now occupied by young trees was entirely barren until recently -- and insects thrive there in the absence of birds and other predators. Scientists expect that the problem will straighten itself out eventually when these do arrive.

But an interim solution may lie in the sterile insect technique, which may save the trees until nature finds its own balance between predators and prey in the young woodlands.

This new technique is based on the use of radiation to sterilize flies in the pupal or adult stage. Overwhelming numbers of them are then released in the area to mate with native flies, whose eggs become consequently infertile.

The sterile-insect technique has already proved valuable in controlling various fruit flies as well as moths, mosquitoes, stable flies, boll weevils, screwworn flies, and horn flies.

The method is an alternative to chemical pesticides, which are becoming more expensive to make because of higher energy costs and which damage the environment as well.

North Africa's transcontinental green belt, stretching from the Nile to the Atlantic, embraces farmsteads, rangeland, and shelter- belts. A master plan incorporating the national land-reclamation policies of several North African countries has grown from a 1977 UN conference on deserts held in Nairobi, Kenya.

Here's what some of these countries are doing:

* Scientists in Egypt are doing research on sand dune stabilization, soil conservation, and afforestation.

* Algeria has contributed the experience gained in a big program aimed at the establishment of a green belt 950 miles long and up to 14 miles wide, protecting a zone of young orchards from the desert sands.

* Tunisia has an elaborate mixture of afforestation, with breaks, range management, and soil conservation to preserve the ecological balance of 62 million acres threatened by the desert. Also in Tunisia the UN World Food Program is sponsoring a project for the construction of dikes to protect oases from the Sahara.

* The Libyans have established some of the largest nurseries in the world to provide for a very ambitious program of afforestation and sand dune stabilization.

* Morocco has several large-scale afforestation programs forming a mozaic pattern of windbreaks and forest areas.